In data communication systems where mobility is required, peripheral devices, such as, broadband modems, may be used which allow wireless communication between an information handling system and a remote device. Specifically, a wireless modem incorporated in the customer premium environment (CPE) couples wirelessly to a wireless access termination system or wireless base station through at least one antenna. The clock or timing within the wireless access modem must be the same as that in the wireless access termination system prior data transmission. Thus, synchronization is performed when the system is powered up.
Wireless modems may be designed for asynchronous or synchronous data transmission. Asynchronous transmission is also referred to as start-stop or bursty transmission, and is usually employed by unbuffered terminals where the time between character transmission occurs randomly. Thereby, the data that flows from a wireless access modem to an information handling system or wireless access termination system will be a bursty, asynchronous data transfer. This data transfer indicates an upstream flow of data. Conversely, data flowing from the wireless access termination system to the wireless access modem indicates a downstream flow of data. This data transmission is a synchronous continuous stream of data. Accordingly, downstream traffic flows at a constant rate and requires synchronization.
Synchronous transmission between modems or other communications devices provides a continuous bit stream of information. No start and stop bits are required to delimit individual characters as in asynchronous transmission. The digital data may be arranged in data symbols and encoded using any number of the various known techniques. Groups of data symbols are formed into encoded data blocks with the length of the block varying from a few characters to a thousand or more. The receiving modem or communication device decodes the data symbols to obtain the original digital data. Each modem or communication device provides a timing signal or clock that is used to establish the data transmission rate and to enable the devices attached to the modems to identify the appropriate bits in each character as they are being transmitted or received as is disclosed in U.S. Pat. No. 6,332,009, which is incorporated by reference herein. Thus, encoded information bits in data symbols are arranged such that they concurrently convey synchronization or timing information to the modem receiving the signal. Synchronization conveying data symbols may be transmitted during an initialization or synchronization procedure or periodically during a resynchronization period performed during a given data transmission session. In some instances, timing may be provided by the terminal device itself or a communication component, such as a multiplexer or front-end processor channel. Regardless of the timing source, the transmitting and receiving devices must establish synchronization among themselves prior to commencing the transmission of data.
A wireless access modem is generally comprised of four components: a transmitter, a receiver, a modem control block and a power supply. The receiver section is responsible for maintaining synchronization using a channel acquisition algorithm after a coupled transmitter has sent a synchronization signal. Generally, the receiver includes an equalizer, a timing recovery module, a demodulator, a descrambler and a DTE interface. In some wireless modem designs, a Reed Solomon decoder couples to receive the descrambled signal to provide error correction in the signal according to known principles. In addition, this module provides Forward Error Correction (FEC) validity or lock indication to an associated controller unit located within the modem. Reed-Solomon error correction is a known type of FEC. The FEC lock indication signals that the Reed-Solomon error correction is synchronized to the data being corrected and is providing valid output.
Moreover, the Reed Solomon decoder may include a Moving Picture Experts Group (MPEG) Protocol Interface (MPI) which represents the last module within the physical layer of the data protocol. The MPI generates 144 bytes per frame for broadcasting the data and a synchronization (sync) byte is used to detect if the frame is synchronized. A media access control (MAC), the second lower layer in the data protocol, couples to receive each frame from the MPI to control when media may be accessed. The host interface couples between the MAC and a personal computer or peripheral device.
Typically, synchronization is lost as a result of signal fading. Signal fading occurs when there is interruption in the signal which leads to a disconnect of the synchronization. Conventionally, the loss of a synchronization may be detected in either one of two ways. First, while monitoring the signal power, a loss of synchronization occurs when the synchronization track of an automatic gain control (AGC) has failed as shown in U.S. Pat. No. 6,332,009. Second, by monitoring when either the Reed Solomon decoder or MPI has lost synchronization. If the sync byte is not detected while monitoring the MPEG Protocol Interface (MPI) sync byte or the Reed/Solomon decoder is not synchronized, the system assumes that the synchronization is lost. Accordingly, the channel acquisition algorithm is restarted or a system reboot is begun; either of which is communicated to the MAC. Thereby, the user of the computer system is alerted and service is interrupted. This interruption in service is an annoyance to the user. Moreover, this approach is lengthy; and, as a result, negatively affects time, cost, and performance.
Therefore, a need exists for a method and apparatus for resynchronization that may recover the synchronization within a predetermined unit of time without the layers above the physical link layer having knowledge.